So I'm feeling the effects but not as much as a full shell which is pretty obvious. I'm around the 15 min point and got that nice little rush of euphoria that PP gives around that time. It's more subtle than usual as you would expect but still noticeable which is pleasant. So maybe repeated shells will just keep the pleasant effects going for longer but at a more subtle level, nice and relaxed, no blast.
The other thing I have thought of is to drink a full shell, nice and strong to start with and then drink half shells as a "maintenance dose". For tonight I'm going to stick to the plan, waiting a little while for the next one.